Abstract: The analysis of coastal erosion and accretion, based on the remote sensing water line, is better than that using field observations because of its convenience, quickness and more data. However, this method hasn’t been applied to Haikou Bay. Four types of water index for extracting waterline from Landsat sensing image are checked by observations in Haikou Bay, in which the water index of NDWI is proved to be the best. The waterlines of 15 Landsat sensing images in 1994—2013 are extracted by NDWI, with which the evolution of the beach slope between high tidal level and low tidal level is analyzed. And the results show that the beach slope is basically stable with the value of 3.7~4.2°. Then the coastal erosion and accretion are analyzed using the extracted waterlines and the beach slope. The character of erosion and accretion isn’t uniform in the beach. Xixiu Beach and Jiari Beach have been eroded, and the eroded depth is 0.36 m near the high tidal level and 0.30 m near the low tidal level, the eroded speed is 1.9 cm/a near the high tidal level and 1.8 cm/a near the low tidal level.

Key words: Haikou Bay, remote sensing, waterline, erosion and accretion, water index